The present invention relates to a pressure switch assembly which is actuated in response to a certain pressure in a pressure line.
Pressure switches of this type are known which comprise a switch housing having a sensing or activating element. The sensing element is exposed to pressure from a pressure line, and a spring acts against the sensing element to resist the pressure. The spring bias defines the switching point. The sensing element is arranged to contact a switching element of an electric switch located in the housing. The spring abuts against a stop ring which is adjustable by a threaded screw to vary the switching point. A cover is provided to retain the electric switch in the housing (see German Patent AS-No. 19 40 338).
In the known configurations a cylindrical switch housing is provided, in the upper part of which the electric switch is located, secured by the cover. Axially therebeneath is provided the stop ring which is guided in a cylindrical recess of the switch housing. The spring pushes the stop ring against a mushroomshaped sensing element exposable to pressure. An adjusting screw protrudes laterally into the switch and against the stop ring. The position of the stop ring, and thus the switching force actuating the switching process, may therefore be adjusted by the operation of the adjusting screw. A disadvantage of this configuration is that the pressure switch is too bulky for a number of applications, due mainly to the laterally projecting adjusting screw. A further disadvantage involves the fact that the contact-closing distance, and thus the switching hysteresis, cannot be altered after installation, as the electrical switch itself is seated fixedly in the housing.
Pressure switch configurations are also known (German Patent OS-No. 33 11 083) in which a lever gear is inserted between a membrane-type sensing element exposed to pressure, and the switching element of the electric switch. The transmission ratio of the gear may be varied from the outside. Such a configuration has the advantage that the switching hysteresis of the electric switch is adjustable, but the switch built in this manner is very expensive and may be prone to failure in certain applications due to its complex design.
The afore-mentioned configurations have in common the fact that the switching pressure may be adjusted at any time from the outside, which in the case of certain switches is undesirable, if a certain predetermined switching point has been set.
It is, therefore, an object of the present invention to design a pressure switch of the aforementioned type so that, the switching point may be adjusted in a very simple manner, after the thus-set switching point cannot be altered or can be altered only by means of special tools.